Problem Weeds Guide - Millennium · PDF fileThe good news is that most weeds do not compete...

Roots Neighborhood Habitat

Problem Weeds Guide

Illinois Department of Natural Resources

Coastal Management Program

Roots Neighborhood Habitat Problem Weeds Guide Updated April 8, 2014

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Introduction This guide will introduce some basic botanical concepts that can help you identify and control weeds in a

garden setting. The guide starts with basic plant anatomy, and then discusses the four most commonly

used weed control methods. A section covering the weeds most commonly found in urban settings

contains illustrations, descriptive information, and the best control method for each plant.

A weed is a plant that grows where a person doesn’t want it to grow. In your wildflower garden, you’ll

use the word “weed” to describe any plant that you didn’t put into the ground. In a garden, weeds can

hoard water and nutrients and shade out your native plants, eventually taking over.

The good news is that most weeds do not compete well with native plants. Within 3 years, 90% of the

weeds in your garden should be under control, with a bit of diligence on your part.

There are nearly 1,000 plants in the Chicago area that one might call “weeds”. Most of them are

adapted to grow in low-nutrient, disturbed soils. In other words, most soil that you’d find in a city.

Many of these plants can grow in sidewalk cracks, which tells you just how adapted they are to living in

unforgiving places.

Most of these plants seldom become a problem and can be easily controlled. A few can become

invasive and will quickly take over a garden, much in the same way they will take over a natural area or a

farmer’s field. Knowing how to recognize these plants and control them is important.

There are three types of life cycles in plants, and the best control method for a weed will depend on its

life cycle.

Annuals are plants that sprout from seed and flower in a single growing season. Pulling and

cutting is the best way to control them.

Biennials are plants that grow a rosette or non-flowering stem in the first year, then flower in the

second year before dying. Spading is the best way to control them.

Perennials are plants that flower for multiple years with the roots surviving over winter. Because

of extensive root systems, perennials are the most problematic of garden weeds. Perennials vary

in their best control method, but frequently herbicide is the best way to control them.

Regardless of the type of plant, a weed should be removed before it sets seed. When a plant’s seeds

mature they typically fall to the ground near the parent plant. Some plants can produce over 10,000

seeds. By removing the seed source, the weed can eventually be controlled. Once a flower is pollinated

it can produce seed even if the plant is killed. Always dispose of flowering weeds in the trash instead of

with yard waste, so that the seeds are not spread elsewhere.

Plants are most vulnerable when getting ready to flower. Cutting, spading, or using a weed killing

herbicide is best done at these times.


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Terminology To effectively control weeds, it is helpful to know basics of plant anatomy. Terms that are good to know

are shown below.

Leaf: the parts of a plant where energy is produced. Most store-bought herbicides are absorbed into

the plant through the leaves.

Rhizome: an underground, horizontal stem that produces new above-ground growth away from the

parent plant.

Root: the part of the plant that anchors it to the ground, takes up water and nutrients from the soil, and

stores energy.

Taproot: a large root that smaller roots grow off of, for example, a carrot

Root Crown: the top part of the root, nearest the surface of the soil. Stems grow from the root crown.

Stem: the above-ground portion of the plant that provides support to branches, leaves and flowers.


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Treatment Methods There are four treatment methods that you can use to control nearly every weed you will encounter in

your garden. Cutting and pulling is effective on annuals and some perennials. Spading is effective on

biennials and some perennials. Herbicide is effective against perennials. When removing weed material

that is in flower, dispose of plants in trash bags instead of with yard waste. Pollinated flowers can

continue to produce seed even when removed from the ground, and compost piles do not get hot

enough to kill the seeds.

CUTTING Cutting is an alternative to pulling that minimizes soil

disturbance. Pulling may also stimulate new growth if the

stem or root is broken. Cutting a stem weakens the plant

and makes it less likely new growth will be generated.

Cutting is best done with a garden shear. Plants should be

cut as close to the ground as possible. If plants are not in

flower, you can leave the cuttings on the ground as natural

compost.

SPADING Spading is done mainly on biennial plants. The process

separates the root crown from the root, keeping new stems

from growing.

Spading can be done with a garden spade or hand spade.

The tip of the spade should be placed against the root,

slightly below the surface of the soil. Apply a downward

thrust at a 30-45 degree angle to cut through the root.

PULLING Pulling can be used on weeds that have shallow root

systems or short taproots. When pulling, the important

thing to keep in mind is not to break the stem from the

root. Otherwise the plant may grow a new stem. Grasp the

stem near the root crown, where the stem is the strongest

and the force of pulling will be transferred to the root.

Pulling can be made easier with the help of a dandelion digger. These hand tools have a curved blade

with a prong at the end. They are designed to give extra leverage when pulling a plant out of the ground.

The tool is used by wedging the prong underneath the root crown, which is usually thicker than the

stem. Applying downward pressure on the handle lifts the pronged end, and the weed along with it.

Once loosened, the weed is much easier to pull from the ground.


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Step 1: wedge the digger against the root, just underneath the top of the soil.

Step 2: Press down on the handle of the digger to lift the plant up out of the soil.

HERBICIDE

For some perennial weeds, herbicide may be the best method of control. In most garden settings, an

herbicide called glyphosate is the safest to use. It is an herbicide that spreads throughout the tissue of

the plant. It can be purchased at most lawn and garden stores under various product names, Roundup

being the most well-known brand. These store-bought mixes are designed for spraying onto the leaves

of the target plant, and the area is safe for people to enter within an hour. Glyphosate breaks down

quickly in soils. Glyphosate is also a non-selective herbicide, meaning it will kill any plant that is sprayed.

Use care with this and any other herbicides to make sure you are not killing desirable plants. An

experienced lawn and garden supply store can offer more assistance if you find the need to use

herbicides.

Always follow label directions with herbicides to avoid using too much or exposing yourself to the

chemicals. Wear eye protection such as safety glasses, rubber gloves, a long-sleeved shirt and long

pants when working with herbicides.


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How to Use This Guide The plants in this guide represent weeds that are commonly seen in garden settings. They are arranged

by several leaf traits. Traits are listed in the following order:

1. Alternate, Opposite, Whorled

Alternate: only one leaf grows from a point on the stem; appear spirally arranged

Opposite: two leaves grow from a point on the stem, directly across from each other

Whorled: three or more leaves grown from a point on the stem, spaced apart evenly

2. Simple or Compound

Simple: each leaf has a single blade

Compound: each leaf has multiple tiny blades called leaflets

3. Shape, from narrowest to widest

Linear: grasslike

Oblong: outstretched

Lanceolate: lance-shaped

Ovate: teardrop-shaped

Elliptic: oval

Sagittate: arrowhead

Hastate: wined

Deltoid: triangular

Cordate: heart-shaped

Reniform: fan-shaped

Orbicular: round

Narrow Oblong Lance-shaped Teardrop (Linear) (Oblong) (Lanceolate) (Ovate)

Oval Arrowhead Winged Triangular (Elliptic) (Sagittate) (Hastate) (Deltoid)

Heart-shaped Fan-shaped Round (Cordate) (Reniform) (Orbicular)


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The leaf traits covered on a particular page appear at the top of each page.

If you have a plant you suspect to be a weed:

1. Note the three traits mentioned on the previous page.

2. Take a photograph of the leaf. Putting the leave against a solid-color background will help bring

out details.

3. Use the keywords at the top of the page to match the leaf/plant to the description.

4. Check the native plant guide as well to eliminate possible native lookalikes.

5. If you still are not sure, check with a University of Illinois Extension office, or refer to online

weed resources.

Each plant description has the common name and the scientific name for each plant. Sometimes the

scientific name will have the abbreviation “sp.” This means there are several closely related species

with similar traits that can be controlled in the same way. The guide also ranks the level of weediness

for each species:

Low: plant is not likely to take over a garden and can be easily controlled.

Medium: plants can be controlled but it will take some time, possibly more than a year

High: plants can quickly take over a garden if not removed. Control can take multiple years.

Some plants are marked as “noxious weeds.” Noxious weeds must, by law, be controlled by the

property own if found on their property. Those labeled “invasive” have the ability to quickly

overrun an area and crowd out all other vegetation.

The best control methods for each plant are listed, along with several distinguishing traits that should

make identification of a plant easier.

Alternate Simple Linear, Oblong

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Yarrow (Achillea millefolium) – perennial

Weediness: low

Control Method: cutting, pulling

Distinguishing Traits:

-white flowers

-feathery leaves, 3-10” long

-sage-like scent when crushed

A perennial weed that spreads via rhizomes. This plant has feathery leaves and small, white, 5-petal flowers. When not in bloom, the plant produces a number of leaves in a cluster low to the ground. Crushed leaves smell like sage. Yarrow can be easily controlled with repeated cutting. Plants can be pulled if growing in open ground. Rhizomes break easily and may generate new growth.

Canada Thistle (Cirsium arvense) - perennial

Weediness: high, NOXIOUS WEED

Control Method: herbicide


-pale pink flowers smaller than other thistles

-short spines on leaves

-no spines on the stems

A weedy perennial thistle that can invade gardens and lawns as easily as vacant lots. Produces branching stems that can flower any time of the year. Other weedy thistles have spiny stems; Canada thistle does not. The leaves are a light green color underneath that sometimes appears ashen. Because of a dense, deep root system, herbicide is the best control method. Cutting will set the plant back but not eliminate it.

Alternate Simple Oblong

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Nodding Thistle (Carduus nutans) - biennial

Weediness: low

Control Method: spading


-magenta flowers

-flower head droops down

-long spines on leaves and stems

The leaves, stem, and flower head of this biennial thistle are covered with long, sharp spines. It produces a whorl of deeply cut spiny leaves, up to 2 feet in diameter, in the first year of growth. A biennial with a large taproot, first and second-year plants can usually be killed by spading.

Bull Thistle (Cirsium vulgare) - biennial

Weediness: low

Control Method: spading


-magenta flowers

-flower head held straight up

-long spines on hairy leaves and stems

This biennial thistle is spiny all over: leaves, stems, and flower head. Leaves and stems are also hairy. A biennial, it produces a whorl of deeply cut spiny leaves in the first year of growth. The whorl stays green through winter and can reach 3 feet across. A biennial with a large taproot, first and second-year plants can usually be killed by spading.

Alternate Simple Oblong

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Curly Dock (Rumex crispus) - perennial

Weediness: low

Control Method: spading, pulling


- curled leaves that resemble cooked bacon

-diminutive yellow-green flowers

-stems and flowers turn rich brown when they mature

This perennial weed produces a whorl of wavy-edged leaves in the spring. In summer, it sends up a flowering stem with clasping, spirally arranged leaves. The small, yellow-green flowers turn a distinctive rust color as seeds ripen This perennial has a large taproot and can be controlled by spading or pulling with the help of a dandelion digger. There are several Rumex plants that get weedy. All have similar leaves and the same yellow-green flowers.

Siberian Elm (Ulmus pumila) - perennial

Weediness: moderate

Control Method: pulling


-numerous alternate leaves on gray branches

-leaves greenish-gray underneath

-disk-shaped winged seeds

A parkway tree whose seeds often blow into gardens and germinate in open soil. The leafy ash-gray woody stems of seedlings are distinct. The sawtooth-edged leaves are a grayish green underneath, between 1-2 inches long. Plants should be pulled using a dandelion digger as soon as they are found. Seedlings left for 3-6 months are difficult to pull because of rapid root growth. Cutting is ineffective, stimulating growth of multiple stems. Winged seeds germinate quickly and should be removed from a garden if they land.

Alternate Simple Lanceolate

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Asiatic Dayflower (Commelina communis) - perennial

Weediness: low



-waxy leaves 1-4 inches long

-2-petaled purple flowers

-forms colonies

The dayflower has distinct purple flowers with two petals. Flowers only last a day before closing. It spreads via rhizomes and quickly forms colonies in areas of open soils. Leaves have a waxy texture and a swollen joint where they clasp the stem. The plant is weakened by cutting and can be eliminated if re-sprouts are quickly cut. Roots are shallow and the plant can be pulled if it is growing by itself in open ground.

Mustards (Brassica sp.) - biennial

Black Mustard (Brassica nigra)

Weediness: low



-irregularly lobed leaves

-4-petal white or yellow flowers

-long upright seed pods

Several members of the mustard family grow as garden weeds. All are biennial plants that in the 1st year produce rosettes of long leaves with erratic lobes that resemble radish or mustard greens. Leaves on flowering stems are sparse with fewer lobes. All mustards have 4-petaled, cross-like flowers that are either yellow or white. Mustards have shallow taproots and are easily pulled. Pods split when ripe and spread seed several feet away from the plant. Plants with seed pods should be discarded with trash instead of yard waste/compost.


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Horseweed (Conzya canadensis) - annual

Weediness: low

Control Method: pulling, cutting


-very tall (up to 6 feet)

-densely spiraled lance-like leaves

-white flowers that partially open

Horseweed is a native wildflower fond of barren soil and open ground. It sprouts in late spring and grows quickly. The numerous lance-shaped leaves are arranged spirally on the stem. The small white flowers appear late summer, and never fully open. Horseweed has shallow roots and can be pulled with little soil disturbance. Cut stems may resprout, but the new growth seldom gets tall. The plant produces thousands of seeds that usually fall near the parent plant. It can quickly colonize the open ground of a garden.

Tall Goldenrods (Solidago altissima, S. canadensis) - perennial

Weediness: medium

Control Method: cutting, herbicide


-feathery plume of small yellow flowers

-leaves with prominent saw-toothed margins

-stems often form galls (see description below)

Tall goldenrods are native perennial wildflowers that produce 3-5 foot stems of spirally-arranged leaves, 1-4 inches long. The leaves have a saw-toothed edge. Showy plumes of yellow flowers bloom in early fall. The plants spread via rhizomes and form large colonies. Plants often develop ball-like galls along the stem from the larvae of harmless gall wasps. Tall goldenrods look similar to horseweed but as perennials can be harder to control. A plant can form a large colony in several years. Tall goldenrods do not take well to being cut. Plants cut twice a year (in July and again before flowering) typically die out after 2-3 years.


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Evening Primrose (Oenothera biennis) - biennial

Weediness: low

Control Method: spading, pulling, cutting


-yellow 4-petaled flowers that open at night

-numerous spirally arranged leaves

Evening primrose produces a dense rosette of lance-shaped, light green leaves in the 1st year. These leaves are usually toothed and often have a reddish midvein. The 2nd year plant produces a 3-5 foot flowering stem with numerous 4-petaled yellow flowers. Both flowers and leaves are spirally arranged on the stem. Evening primrose is a native wildflower adapted to disturbed areas. Spading will usually kill the plant. Evening primrose has an 8-12 inch taproot; cutting often triggers resprouting. If pulling, use a dandelion digger.

Dame’s Rocket (Hesperis matronalis) - biennial

Weediness: medium, INVASIVE

Control Method: spading, cutting, pulling


-purple or pink 4-petaled flowers

-stems dense with spirally-arranged leaves

-1st year rosette stays green over winter

Dame’s rocket produces a rosette of numerous lance-shaped leaves in its 1st year. In spring of the 2nd year, it produces a 2-3 foot stem. The 2nd year leaves are more pointed than the 1st year rosette leaves. The purple or pink flowers resemble garden phlox, but have 4 petals instead of 5. The 1st year rosettes can be spaded or pulled with a dandelion digger. The 2nd year plants can be spaded, cut, or pulled. Cutting is best done before the flowers open. Seeds can be scattered up to 15 feet from the parent plant, helping this plant to quickly take over open areas.


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Chicory (Cichorium intybus) - perennial

Weediness: medium



-dandelion-like basal leaves

-shrubby stems with tiny leaves

-lavender-blue flowers

Chicory has deeply cut leaves near the base of the stem that look like dandelion leaves. Closer to the top, the stem-clasping leaves become short and stubby. Stems are tough and woody with bristly hairs. The blue flowers appear in summer and blooming may persist into fall. Chicory is a perennial that seldom invades gardens but is tough to get rid of once established. The dense root system makes it hard to pull. Repeated cuttings eventually set it back. Herbicide applied to the basal leaves early in the year is effective.

Mullein (Verbascum thapsus) - biennial

Weediness: low

Control Method: pulling, spading


-light green leaves covered with soft, dense hairs

-tightly-packed spike of 5-petaled yellow flowers

No other weedy plant resembles mullein. The furry light green leaves resemble a lamb’s ear. The first year rosette can grow as large as 3 feet across. In the second year, a single flower spike with hundreds of pale yellow flowers grows up to 7 feet tall. Mullein is easily controlled in a garden. Plants have a shallow fibrous root system. Pull 1st year plants with a dandelion digger. Spade 2nd year plants when the flowering stem starts to grow.

Alternate Simple Ovate

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Lamb’s Quarters (Chenopodium album) - annual

Weediness: low



-light green, toothed leaves

-tiny dull white flowers

Lamb’s quarters is the most common of several Chenopodum that grow as garden weeds. All have light green toothed leaves and tiny white flowers. Leaves get narrower towards the top of the plant. The dull white flowers are surrounded by protective leaves that give them a greenish appearance. These annual weeds have shallow root systems and are easily pulled. Cutting is also an effective control method.

Pokeweed (Phytolacca americana) - perennial

Weediness: low



-Knob-like white flowers and berries

-broad oval leaves

-tall (up to 7 foot) hollow stems

Pokeweed is a native perennial wildflower that invades slightly shaded areas. The broad teardrop-shaped leaves somewhat resemble a milkweed, though they are arranged spirally on the stem instead of opposite. The white, knob-like flowers appear in summer and ripen into deep blue berries. The flowering stem is often reddish. Pokeweeds have large taproots that can grow to the size of a softball. Pulling is difficult. Plants can be controlled by cutting, but will persist for several years. Herbicide applied to the re-sprouts that appear after cutting is highly effective.


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Climbing Nightshade (Solanum dulcamara) - perennial

Weediness: low

Control Method: cutting, pulling, herbicide


-vine with woody stems

-bright purple and yellow flowers

-leaves with lobes at 90o angles

Climbing nightshade invades gardens, shaded ground and hedges. The poisonous plant has a woody stem with light brown bark. Older leaves have lobes set at 90o angles. The purple flowers resemble those of a tomato, a close relative. Red berries quickly ripen to a deep purple. Climbing nightshade has brittle roots. Cutting is effective, but may need to be done several times a year to kill the plant. If plants are pulled, use a dandelion digger to keep the root from breaking. Herbicide applied to re-sprouting foliage is highly effective.

Black Nightshade (Solanum nigrum) - annual

Weediness: low



-shiny pointed leaves similar to tomato leaves

-tiny white flowers

-small purple berries

This common, poisonous weed looks like a small tomato, a plant to which it is closely related. Seldom more than 1 foot tall, the shiny pointed leaves are often covered in holes from insect browsing. The plants bloom in summer and produce dark purple berries in early fall. Black nightshade is easily controlled by pulling. The roots are weak and shallow and pull with little soil disturbance. Cutting also eliminates the plant.


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Horsenettle (Solanum carolinense) - annual

Weediness: low



-crooked stem

-deeply-lobed leaves

-white tomato-like flowers

Horsenettle is a relative of the tomato family that occasionally invades gardens from vacant areas. It has a crooked, hairy stem similar to a tomato vine. The deeply-lobed leaves are distinct. The white flowers ripen into yellowish berries in the fall. Horsenettle is easily controlled by pulling. The roots are weak and shallow and pull with little soil disturbance. Cutting also eliminates the plant.

Mercury (Acalypha sp.) - annual

Weediness: low



-tiny green flowers up and down the stem

-sticky stems, leaves and seeds

There are several species of native wildflowers called mercury that grow as garden weeds. Seldom more than 1 foot tall, plants have lance or oval-shaped leaves with saw-tooth edges. The tiny green flowers grow from the same points as the leaves, and are wrapped around the stem. All parts of the plant are covered in fine hairs that stick like Velcro. All mercury plants have shallow roots and can be pulled without soil disturbance. They can also be cut.

Alternate Simple Ovate, Sagittate

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Purselane (Portulaca oleracea) - annual

Weediness: low



-mat-like growth

-fleshy leaves

-small yellow flowers

This mat-forming weed is common in open ground. The fleshy, almost succulent leaves are alternating on the stem. The small yellow flowers grow along stems and bloom throughout summer. Purselane roots are shallow and can be easily pulled. They can’t compete with tall plants and get crowded out as gardens get established.

Field Bindweed (Convulvulus arvensis) - perennial

Weediness: high, NOXIOUS WEED

Control Method: herbicide, cutting


-twining vine

-arrowhead-like leaves

-white or pink bell-shaped flowers

Bindweed is a twining vine that wraps itself around anything it comes in contact with. Stems emerge in spring and grow as much as an inch a day. It also spreads via underground rhizomes and deep roots. The white, bell-shaped flowers appear in early summer. The arrowhead-shaped leaves are distinctive. Bindweed is one of the most difficult weeds to control once established. Repeated cutting will weaken the plant and take 3-5 years to kill it. Herbicide is highly effective on plants that are not climbing up desirable vegetation. DO NOT PULL! Rhizomes are brittle and break easily, resulting in multiple stem re-sprouts.

Alternate Simple Cordate

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Morning Glory (Ipomoea sp.) - annual

Weediness: low



-twining vine

-heart or ivy-shaped leaves

-pink (sometimes purple or white) flowers

Morning glory is a twining vine that wraps itself around anything it comes in contact with. Leaves are usually heart-shaped or ivy-shaped. The large trumpet-shaped flowers are usually pink, but can range from purple to white. Morning glory is an easily-controlled annual. Most have bulbous taproots and cutting is the best control method. Pulling with the aid of a dandelion digger is also effective. Pull vines early in the year before they have a chance to strangle desirable plants.

Velvet Leaf (Abutilon theophrasti) - annual

Weediness: low



-velvety heart-shaped leaves

-yellow flowers hidden behind leaves

No other plant, native or weed, has leaves with the texture that give velvet leaf its name. It is usually found growing in open ground, and is usually seen in recently established gardens. Flowers are often hidden behind the large leaves. Velvet leaf can be easily controlled by cutting. An annual with a weak root system, it seldom re-sprouts.

Alternate Simple Cordate

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Garlic Mustard (Alliaria petiolata) - biennial

Weediness: high, INVASIVE

Control Method: pulling


-heart-shaped leaves with blunt-tooth margins

-garlic-like scent when crushed

-small white 4-petaled flowers

Garlic mustard is a biennial weed that will appear in shaded gardens and along hedges. A dense rosette of rounded heart-shaped leaves grow in the 1st year, staying green over winter. A flowering stalk with pointed heart-shaped leaves grows in the 2nd year, with a spike of small white flowers. Garlic mustard flowers in mid-spring. Garlic mustard is highly invasive in wooded areas. If found in a garden setting it should be immediately controlled. The roots are shallow and the plant can be pulled. Seeds scatter up to 15 feet from the parent plant. Any plants in flower or with seed pods should be disposed of with trash.

Japanese Knotweed (Polygonum cuspidatum) - perennial




-heart or triangle-shaped leaves with squared bases

-tall stems with red blotches

-spikes of tiny white flowers

Japanese knotweed forms large colonies with stems exceeding 10 feet tall. Stems are hollow with red blotches. The heart-shaped leaves have blunt bases. The small white flowers appear in mid-summer on upright spikes along the length of stems. Japanese knotweed is highly invasive. Root systems are extensive and deep and can damage building foundations. To control, spray plants with an herbicide early in the year when still low to the ground. Cutting taller stems and spraying re-sprouting stems is also effective. Even with herbicide it can take 3-4 years to kill a single plant.

Alternate Simple Deltoid

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Flower-of-an-hour (Hibiscus trionum) - annual

Weediness: low



-lobed leaves with blunt-toothed margins

-white flower with purple accents

Rose mallow is a fast-growing summer annual. The triangular, lobed leaves with round-toothed margins are unique amongst garden weeds. The white flowers with purple accents stay open for less than a day. Rose mallow has a short taproot and can easily be pulled. Cutting is also effective; plants seldom re-sprout.

“Grass” Clovers (Trifolium sp.) - perennial

Weediness: low



-typical 3-parted clover leaf with oblong leaflets

-short spike of pink, white, or yellow flowers

-leaflets often have a v-shaped “watermark”

“Grass” clovers were originally mixed in with lawn seeds and are now common in gardens. They grow in low clumps, usually 1 foot tall or less. Leaves are the typical 3-parted clover leaves. Most species have a v-shaped “watermark” on leaflets. The small, ball-like spike of flowers appears in early-to-mid summer. Grass clovers are easily controlled by cutting. The fibrous roots are shallow but spreading; pulling may disturb soil. Clovers compete poorly against taller vegetation, but their ability to fix nitrogen to the soil helps other weeds invade open ground.

Alternate Compound Oblong

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Sweet Clover (Melilotus officinalis., M. albus) - biennial




-tall, branching, woody stem

-spikes of small, white or yellow flowers

Sweet clover is a biennial that puts up stems in both years of growth. First year plants are low-growing, usually 6-12 inches tall. Second year plants can exceed 6 feet and are branching. Two species of sweet clover occur as weeds: one with white flowers, the other with yellow flowers. The plants otherwise look identical. Both bloom in early summer. Sweet clovers are invasive in natural areas but seldom more than a nuisance weed in gardens. Do not allow sweet clover to set seed. Seeds can survive over 30 years in the soil.

Crown Vetch (Securigera varia) - perennial




-short, bushy growth

-compound leaves with 11-25 leaflets

-large ball of pink flowers

Crown vetch is a spreading, bushy clover. Seldom more than 2 feet tall, plants can form a shrub-like cluster up to 6 feet in diameter. The dark green leaves have 11-25 leaflets. A cotton ball-sized cluster of pink flowers appears in early summer. Crown vetch is highly invasive in natural areas. It often invades gardens from alleyways and roadsides. Its extensive root system helps it out-compete other vegetation and it resists pulling and cutting. Seedlings and young plants can be pulled. Established plants are resistant to cutting and pulling and are best controlled with herbicide.

Alternate Compound Oblong

22

Sulfur Cinquefoil (Potentilla recta) - perennial

Weediness: low



-5 or 7-part palm-like leaves

-yellow flowers with 5 heart-shaped petals

-hairy leaves and stems

Sulfur cinquefoil grows as a branching, shrubby weed. It produces compound basal leaves, usually with seven oblong lobes with sawtooth margins. Leaves on the hairy stem are usually 5-parted. The yellow flowers with heart-shaped petals bloom through summer. Sulfur cinquefoil can be controlled by cutting. Several cuttings in a growing season are sufficient. Young plants can be pulled. Older plants have an extensive, woody root system and should be cut rather than pulled.

Queen Anne’s Lace (Daucus carota) - biennial

Weediness: low

Control Method: spading, pulling


-lacy leaves

-cluster of white flowers with 1 purple flower in the center

Queen Anne’s lace is the wild version of the carrot. Plants produce a dense rosette of lacy, deeply divided leaves in the 1st year. The 2nd year plants produce a branched stem with only a few leaves. Blooms appear on an umbrella-like cluster of small white flowers, usually with 1 purple flower in the center. Like a carrot, Queen Anne’s lace has a long taproot. Spading will usually kill a plant. Rosettes and flowering plants can be pulled with a dandelion digger. Plants broken above the ground will resprout.

Opposite Simple Oblong, Lanceolate

23

Black Medic (Medicago lupulina) - annual

Weediness: low



-clover-like 3-parted leaf

-small balls of tiny yellow flowers

Black medic looks similar to clovers, though it grows taller, up to 2 feet. The 3-parted clover-like leaves are arranged spirally on the stem. In summer, the plant produces a spike of tiny yellow flowers that look like puffballs. Black medic is related to alfalfa. It long ago escaped hay fields and is now a common weed. Cutting is an effective control. Pulling small plants, before the fibrous roots spread, is also effective.

Wood Sorrel (Oxalis stricta) - perennial

Weediness: low



-clover-like leaf with heart-shaped leaflets

-5-petaled yellow flowers

Wood sorrel is sometimes confused with clover. Sorrel leaves have heart-shaped leaflets in 3-parts, where clover has round or oblong leaflets. The plants are short, seldom more than a foot tall. A native wildflower, wood sorrel can get weedy in the open spaces of a garden. Cutting usually eliminates it after 2-3 cuts in a year. It does not compete well against taller vegetation. If managed, it can serve as a groundcover for a year or two while more desirable plants grow to fill in open spaces.

Opposite Simple Ovate

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Matted Spurges (Chamaesyce sp.) - annual

Weediness: low



-mat-forming

-oblong leaves opposite on stem

-white sap when broken

Matted spurge stems grow along the ground. A single plant can produce up to 20 stems. The small (1/4 inch or less) leaves grow opposite from each other along each stem. Tiny white flowers about the size of a pinhead grow from the tips of the stems. Matted spurges have weak roots and can be either cut or pulled to control. Taller vegetation shades them out, so it rarely persists in gardens.

Ragweed (Ambrosia artemisifolia, A. psilostachya) - annual/perennial

Weediness: low

Control Method: cutting


-deeply lobed leaves

-leaves opposite on main stem, alternate on flowering stems

-small green ball-like flowers

Ragweed is easy to spot in a garden. The leaves tend to be teardrop-shaped with deep lobes. The leaves on the main stem are opposite. On the flowering stems, the leaves are arranged spirally. Floral spikes appear on the tips of branches and are a greenish-white color. Two species of ragweeds will grow in gardens. The annual common ragweed (A. artemisifolia) is usually encountered. Western ragweed (A. psilostachya) is a perennial that forms small colonies by sending out rhizomes from the main stem. Cutting is highly effective against both.

Opposite Simple Sagittate

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Giant Ragweed (Ambrosia artemisifolia) - annual

Weediness: low



-ivy-like leaves with saw-toothed edges

-leaves are opposite on main stem, alternate on flowering stems

-small green ball-like flowers

True to its name, giant ragweed can grow more than 10 feet tall. The oval-shaped leaves develop deep lobes, making them resemble ivy leaves. The leaves are silver-gray underneath. In late summer it produces long spikes of yellow-green flowers. Giant ragweed is seldom found in backyard gardens, but will invade gardens in open areas. Small plants can be pulled. Larger plants, more than 3 feet tall, should be cut.

Cutleaf Teasel (Dipsacus laciniatus) - biennial


Control Method: herbicide, spading


-lettuce-like leaves with netted veins

-spines surrounding egg-shaped flower spike

-leaves clasp stem to form cups

Cutleaf teasel is a biennial, producing a rosette of irregularly lobed saw-toothed leaves in the 1st year. The 2nd year stem has similar leaves that clasp the stem and form a cup that traps water. The flower heads are egg-shaped, surrounded by spike-like projections, and producing small white (sometimes pink) flowers. Teasels are highly invasive and should be removed immediately if found. Spraying herbicide on 1st year rosettes is the most effective control. Spading will weaken the plant but not kill it.


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Black Swallow-wort (Cynachum louiseae) - perennial


Control Method: herbicide, cutting


-oval-shaped opposite leaves

-twirling vine

-pungent smelling dark purple flowers

Black swallow-wort is a branching, twirling vine that can grow 6 feet long. The teardrop-shaped leaves with pointed tips are arranged opposite on the stem. At the tips of branches, dark red-purple flowers bloom in summer. The flowers have a smell that mimics rotting fruit. This plant is a persistent pest. A perennial, it produces a deep, extensive root system making it difficult to control. Herbicide plants in late spring before they climb desirable vegetation. Cutting stems and putting herbicide on re-sprouting leaves is effective. It can take several years to eradicate this plant.

Spearmint (Mentha spicata) - perennial

Weediness: low



-minty scent when crushed

-small pink flowers on thimble-like spikes

-square stems

Spearmint is the most common of several mints that become weedy. It has a square stem with opposite, teardrop-shaped leaves with a toothed margin. The crisscrossing veins give the leaf a net-like appearance. Thimble-like spikes of light pink flowers are born at the top of the plant. Spearmint becomes bushy if left alone. Along with most weedy mints, it can be killed by several cuttings throughout a growing season. Younger plants can be pulled.


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Mouse-eared Chickweed (Stellaria media) - annual

Weediness: low



-small, ovate opposite leaves

-stems that flop towards the ground

-small white flowers with divided petals

Chickweed is a low-grown weed of lawns and gardens. The tiny, oval leaves give the plant its name. Plants form a circular clump of dense stems in late winter. The petals of the small white flowers are divided down the middle, making it look like the flower has 10 petals instead of 5. They bloom in spring. Chickweed becomes weedy in open areas. In gardens it is easily controlled by cutting or pulling. Chickweed competes well with taller vegetation and should not be left to set seed.

Catnip (Nepeta cataria) - perennial

Weediness: low



-sawtoothed triangular leaves

-square stems

-earthy scent when crushed

Catnip is easy to ID in a garden because of its distinct, earthy-mint scent. It has a square stem with opposite, triangular, saw-tooth margined leaves. The leaf veins form a net-like appearance. The small lavender-pink flowers emerge from along the tips of stems. Catnip becomes bushy if left alone. Like most weedy mints, it can be controlled by several cuttings throughout a growing season. Younger plants can be pulled before the spreading root system is well established. Catnip may attract outdoor cats, which will damage other garden plants by trampling.

Alternate, Whorled Simple Lanceolate

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Creeping Charlie (Glechoma hederacea) - perennial

Weediness: medium

Control Method: herbicide, cutting, pulling


-rounded leaves with toothed margins

-spreading rhizomes form a thick mat

-small pink flowers on low stems

Creeping Charlie is a groundcover that escapes gardens and invades open areas. Rhizomes grow roots and leafy stems. The rounded leaves are opposite each other on the square stems. Though a mint, the leaves do not have a scent when crushed. Creeping Charlie will colonize any patch of open ground it is introduced to. Herbicide is the most effective means of control. Cutting and pulling are not always effective, as any broken root or rhizome produces new growth.

Maples (Acer sp.) - perennial

Weediness: moderate

Control Method: cutting, pulling, herbicide


-rounded or triangular lobed leaves opposite on the stems

-“helicopter” seeds

Maple seeds will sprout on nearly any type of moist ground. Seedlings quickly develop an extensive root system. The lobes on the leaves (usually 5) taper to a point. Seedlings can grow more than two feet in a single year. Maples are problems when their single-winged “helicopter” seeds blow into gardens where they quickly sprout. The best control is to remove seeds when they drop, usually mid-summer. Seedlings should be pulled with a dandelion digger, as roots grow quickly.


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Sow Thistles (Sonchus sp.) – annual/perennial

Weediness: medium



-thistle-like leaves that clasp stem

-dandelion-like flowers

The several species of sow thistles all have thistle-like leaves that clasp the stem. The tips of the stems branch, with each branch producing several yellow flowers that resemble a dandelion. Sow thistles tend to bloom in the mid-summer. Whether annual or perennial, sow thistles can be controlled by cutting; even perennial sow thistles are unlikely to resprout. The numerous seeds produced by the flowers are moved around by wind, allowing a single plant to quickly colonize open ground. Pulling established plants, with long rhizomes, may disturb soil.

Dandelion (Taraxacum officinale) –perennial

Weediness: medium

Control Method: spading, herbicide


-non-spiny thistle-like leaves

-yellow flower resemble a sunburst

Dandelions are one of our most common and well-known weeds. Usually growing in the spring, they produce a rosette of deeply lobed leaves that look like they have arrowheads on the tips. Several stems, each with a yellow sunburst flower, emerge in late spring. Dandelions produce a lot of seeds. Do not let them establish in a garden. Pulling should be avoided as the long taproots break easily and then grow a new plant. Spading is sometimes effective if done several times over the growing season. Herbicide is the best way to remove this plant from a garden setting.


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English Plantain (Plantago lanceolata) - perennial

Weediness: low



-Rosette of lance-like leaves with well-spaced teeth

-spikes of tiny white flowers

English plantain is a common sidewalk and garden weed, preferring open ground with little competition. The waxy, lance-shaped leaves have the occasional tooth along the margins. The leaves display prominent parallel veins. The tiny white flowers appear in summer, growing from a club-like flower head. English plantain is seldom a problem in gardens. Plants are easily controlled by cutting. Pulling is effective if no good plants will be disturbed by the upturning of soil. A dandelion digger should be used as leaves and stems break easily.

Hawkweeds (Hieracium sp.) - perennial

Weediness: low



-hairy, lance-shaped leaves

-cluster of small dandelion-like flowers on tip of long stem

Several species of hawkweeds can get weedy in gardens. They produce either a whorl of leaves or have spirally arranged leaves low on the stem. Leaves and stems are always hairy. A long stem with a cluster of dandelion-like yellow or red flowers appears in midsummer. Hawkweeds are common in vacant and untended lots and seeds can blow into gardens. Their fibrous roots compete with surrounding plants. Cutting the plants several times in a growing season generally kills it.


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Common Plantain (Plantago major) - perennial

Weediness: low



-broad oval leaves with prominent veins

-long spike of tiny white flowers

Common plantain is often found in gardens and other open spaces. The waxy, oval leaves have prominent parallel veins and wavy margins. A long spike of tiny white flowers appears in early summer. Plantains are seldom a problem in gardens. Plants are easily controlled by cutting. Pulling is effective if no desired plants will be disturbed by the upturning of soil by fibrous roots. A dandelion digger should be used as the stems and leaves break easily.

Printed by authority of the State of Illinois

May 5, 2014

Problem Weeds Guide - Millennium · PDF fileThe good news is that most weeds do not compete...

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